**3.1 Organochlorines**

These are chlorinated hydrocarbons which represent diverse group of compounds with carbon, hydrogen and chlorine in their structure. They comprise of three subgroups, namely, dichlorodiphenylethanes (dichlorodiphenyltrichloroethane [DDT], dicofol, methoxychlor, and perthane), chlorinated cyclodienes (aldrin, endrin, dieldrin, chlordane, endosulfan, and heptachlor), and hexachlorocyclohexanes (benzene hexachloride [BHC], chlordane, lindane, mirex, and toxaphene) [9]. The only organochlorine compound being used in residual spraying is DDT with 82% of organochlorines compounds being used in Southeast Asian region, mainly India, for vector control. DDT causes the alteration of the sodium and potassium ion transport across axonal membranes; this results in increased negative after-potential and prolonged action potentials, which consequently leads to repeated firing and occurrence of sequential action potentials, thus causing spasms and death of the insect [10]. DDT was first used during World War II for the control of mosquitoes and was extensively used in the period from 1940s to 1960s, and was banned in 1972 by the Environmental Protection Agency (U.S.A.).
